U.S. patent application number 13/146270 was filed with the patent office on 2011-11-24 for imaging element and imaging apparatus using the same.
Invention is credited to Hideaki Hirai, Ryosuke Kasahara.
Application Number | 20110285898 13/146270 |
Document ID | / |
Family ID | 42356045 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110285898 |
Kind Code |
A1 |
Kasahara; Ryosuke ; et
al. |
November 24, 2011 |
IMAGING ELEMENT AND IMAGING APPARATUS USING THE SAME
Abstract
An imaging element includes a light receiving surface having
pixels, and a low-pass filter device configured to focus
predetermined light on a predetermined pixel of the pixels of the
light-receiving surface.
Inventors: |
Kasahara; Ryosuke;
(Kanagawa, JP) ; Hirai; Hideaki; (Kanagawa,
JP) |
Family ID: |
42356045 |
Appl. No.: |
13/146270 |
Filed: |
January 26, 2010 |
PCT Filed: |
January 26, 2010 |
PCT NO: |
PCT/JP2010/051314 |
371 Date: |
July 26, 2011 |
Current U.S.
Class: |
348/360 ;
348/362; 348/E5.024 |
Current CPC
Class: |
H04N 5/238 20130101;
H04N 5/2254 20130101; G02B 5/1885 20130101; H01L 27/14621 20130101;
H04N 9/04557 20180801; H01L 27/14629 20130101; H04N 9/0451
20180801; H04N 9/045 20130101 |
Class at
Publication: |
348/360 ;
348/362; 348/E05.024 |
International
Class: |
H04N 5/225 20060101
H04N005/225; G03B 7/00 20060101 G03B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2009 |
JP |
2009014195 |
Claims
1. An imaging element, comprising a light receiving surface having
pixels; a low-pass filter device configured to focus predetermined
light on a predetermined pixel of the pixels of the light-receiving
surface.
2. The imaging element according to claim 1, wherein the low-pass
filter device is configured to extract a wavelength component of
the predetermined light when focusing the predetermined light.
3. The imaging element according to claim 1, wherein the low-pass
filter device has a polarization-dependent characteristic changing
depending on a polarization direction of the predetermined
light.
4. The imaging element according to claim 3, wherein the
polarization-dependent characteristic of the low-pass filter device
is a characteristic to transmit only a predetermined polarized
light component.
5. The imaging element according to claim 1, wherein the pixels of
the imaging element are divided into a plurality of periods each
having an anomalous pixel; wherein the low-pass filter device has
an LPF characteristic such that a light amount of a light beam
focused on the anomalous pixel configured to extract a
predetermined wavelength component is larger than an average light
amount of light beams of the predetermined wavelength component
focused on pixels adjacent to the anomalous pixel entering within
one period of the pixels of the imaging element.
6. An imaging apparatus comprising a lens system; an imaging
element configured to image a subject to form a subject image via
the lens system; and a control device configured to process the
subject image as image data, wherein the imaging element includes a
light receiving surface having pixels and a low-pass filter device
configured to focus predetermined light on a predetermined pixel of
the pixels of the light-receiving surface; wherein the control
device is configured to perform a separation process to separate
the subject image formed by the imaging element into a first image
formed by the predetermined pixels and a second image formed by
pixels other than the predetermined pixels.
7. The imaging apparatus according to claim 6, wherein the first
image is an image regarding color information and the second image
is an image regarding brightness information.
8. The imaging apparatus according to claim 6, wherein the first
image is an image regarding polarization information and the second
image is an image regarding brightness information.
9. The imaging apparatus according to claim 6, wherein the control
device is configured to perform an image expansion process to
generate a fourth image by expanding the first image and an image
composition process to compose the second and fourth images to form
a third image in addition to the separation process.
10. The imaging apparatus according to claim 9, wherein the control
device is configured to perform an image conversion process to
convert color information of the second and third images into
brightness information and to form a fifth image having brightness
values of RGB in addition to the image expansion process and the
image composition process.
11. The imaging apparatus according to claim 6, wherein the control
device is configured to perform an image reduction process to
reduce the second image to form a fourth image and an image
composition process to compose the first and fourth images to form
a third image in addition to the separation process.
12. An imaging apparatus, comprising a lens system; an imaging
element configured to image a subject to form a subject image via
the lens system; and a control device configured to process the
subject image as image data, wherein the imaging element includes a
light receiving surface having pixels and a low-pass filter device
configured to focus predetermined light on a predetermined pixel of
the pixels of the light-receiving surface; wherein the control
device is configured to perform a separation process to separate
the subject image formed by the imaging element into a first image
formed by the predetermined pixels and a second image formed by
pixels other than the predetermined pixels; wherein the control
device is configured to perform an image expansion process to
expand the first image to form a fourth image, an LPF process to
apply an LPF processing to the second image to form a sixth image
by removing high frequency component from the first image, and an
image composition process to compose the fourth and sixth images to
form a third image.
13. The imaging apparatus according to claim 12, wherein the
control device is configured to perform an image conversion process
to convert color information of the second and third images into
brightness information to form a fifth image having brightness
values of RGB in addition to the image expansion process, the LPF
process and the image composition process.
14. The imaging apparatus according to claim 12, wherein the LPF
process is a process to average brightness values of pixels within
a small range in relation to a period in which the predetermined
pixels are arranged.
15. The imaging apparatus according to claim 12, wherein the LPF
process includes an image reduction process and an image expansion
process.
Description
[0001] This application is based on and claims priority from
Japanese Patent Application No. 2009-014195, filed on Jan. 26,
2009, the disclosure of which is incorporated herein by reference
in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to an imaging element which is
used in an imaging apparatus such as a digital camera, or the like
and an imaging apparatus having the same.
BACKGROUND ART
[0003] Conventionally, for use of a back-monitor of a vehicle, an
high sensitive imaging apparatus capable of obtaining a color image
has been known. Recently, multifunctional imaging apparatus capable
of, for example, imaging a polarized image for detecting a wet
state of a road surface with a high sensitivity has been
required.
[0004] In a conventional technique, when a color image or a
polarized image is obtained, methods for demosicing an obtained
image by providing a color filter on each pixel of the imaging
element (see, for example, Japanese Patent Application Publication
No. 2000-278503), or disposing a micro-polarizer (see, for example,
Japanese Patent Application Publication No. 2007-86720) has been
generally used.
[0005] However, for example when a RGB primary color filter is
used, simply, a light amount received by each pixel is reduced to
one-third of a light amount in a case where the filter is not used.
Furthermore, in a case where a polarizer is used, since only a
light amount of either P-polarized light or S-polarized light, that
is, 1/2 of total light amount is received by each pixel, the light
amount received by each pixel is reduced to 1/2 of light amount in
a case where the filter is not used is received by each pixel.
Therefore, there is a problem in that sensitivity is degraded in
principle. Furthermore, resolution of brightness information is
degraded compared to the case where the filter is not used, so that
low resolution of an obtained image is visible to the human
eyes.
[0006] In order to solve the above problems, regarding a filter
array to obtain an color image, for example, it has been proposed
that pixels without filter are added to a color filter array in
order to obtain brightness information with the fact that
sensitivity of the human eyes to brightness signals is higher than
that to color signals (see Japanese Patent No. 4144630).
[0007] However, in the above conventional technology, there are
problems in that, for example, when combining the brightness
information and the color information, if a sampling period of the
color information is small in relation to the brightness
information, aliasing noise occurring in the color information
causes degrade in a quality of an image so that ratio of the pixels
without filter cannot be increased.
[0008] Furthermore, there is a problem in that due to a large
difference between the receiving light amount of the pixel with a
filter and the receiving light amount of the pixel without a
filter, only the light amount of the pixel without filter is
saturated so that normal color reproduction cannot be achieved.
SUMMARY OF INVENTION
[0009] The present invention is to provide an imaging element
capable of achieving a normal color reproduction as well as high
resolution and sensitivity can be achieved and ratio of pixels
without filter can be increased, and an imaging apparatus using the
imaging element.
[0010] In order to achieve the above object, an imaging element
according to an embodiment of the present invention includes a
light receiving surface having pixels, a low-pass filter device
configured to focus predetermined light on a predetermined pixel of
the pixels of the light-receiving surface.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a schematic configuration diagram of an imaging
optical system having an imaging element according to an embodiment
of the present invention.
[0012] FIG. 2A is a perspective view illustrating a low-pass filter
viewed from a side of a lens.
[0013] FIG. 2B is a perspective view illustrating the low-pass
filter viewed from a side of an imaging element body.
[0014] FIG. 2C is a sectional view illustrating the low-pass
filter.
[0015] FIG. 3A is an explanatory view illustrating a case where
light having wavelengths of 450 nm and 550 nm enters the low-pass
filter on a diffracting surface of the low-pass filter at a side of
a lens.
[0016] FIG. 3B is an explanatory view illustrating a case where
light having wavelength of 650 nm enters the low-pass filter on the
diffracting surface of the low-pass filter at the side of the
lens.
[0017] FIG. 4 is a view illustrating a relationship between a
0-order light transmissivity or a first order light diffraction
efficiency and a groove depth of concave-convex shapes on the
diffracting surface of the low-pass filter at the side of the
lens.
[0018] FIG. 5A is an explanatory view illustrating a case where the
light having the wavelengths of 450 nm and 550 nm enters the
low-pass filter on a diffracting surface of the low-pass filter at
a side of an imaging element body.
[0019] FIG. 5B is an explanatory view illustrating a case where the
light having the wavelength of 650 nm enters the low-pass filter on
the diffracting surface of the low-pass filter at the side of the
imaging element body.
[0020] FIG. 6 is a view illustrating a relationship between a
0-order light transmissivity or a first order light diffraction
efficiency and a groove depth of concave-convex shapes on the
diffracting surface of the low-pass filter at the side of the
imaging element body.
[0021] FIG. 7 is an explanatory view explaining a structure of a
filter array having a period of 6.times.6.
[0022] FIG. 8 is a view illustrating a flow to process an image
imaged by an imaging element.
[0023] FIG. 9 is a view illustrating a flow to process an image
imaged by an imaging element.
[0024] FIG. 10 is a view illustrating a flow to process an image
imaged by an imaging element.
[0025] FIG. 11 is a view illustrating a flow to process an image
imaged by an imaging element.
[0026] FIG. 12 is an explanatory view explaining a structure of a
filter array having a period of 16.times.16 in a second
embodiment.
[0027] FIG. 13 is a view illustrating paths of light beams when
transmitting a birefringent medium.
[0028] FIG. 14A is a view illustrating a diffracting grating which
a light beam enters.
[0029] FIG. 14B is a sectional view along B-B line of FIG. 14A.
[0030] FIG. 14C is a view illustrating a transmitting state
according to a polarization direction of a light beam.
[0031] FIG. 14D is a view illustrating a transmitting state
according to a polarization direction of a light beam.
[0032] FIG. 15 is a sectional view illustrating a low-pass filter
of the second embodiment.
[0033] FIG. 16 is a perspective view of the low-pass filter.
[0034] FIG. 17A is an explanatory view explaining a state where an
extraordinary light beam enters the low-pass filter.
[0035] FIG. 17B is an explanatory view explaining a state where an
ordinary light beam enters the low-pass filter.
[0036] FIG. 18 is a view illustrating a relationship between a
0-order light transmissivity or a first order light diffraction
efficiency of the ordinary light beam and a groove depth of
concave-convex shapes on the diffracting surface of the low-pass
filter at the side of the imaging element body.
[0037] FIG. 19 is a sectional view illustrating a low-pass filter
where diffracting structures are oppositely disposed.
[0038] FIG. 20 is a perspective view illustrating a low-pass filter
having a periodic structure with a period smaller than a
wavelength.
[0039] FIG. 21 is an explanatory view explaining a structure of a
filter array having a period of 6.times.6 in a second
embodiment.
[0040] FIG. 22 is a view illustrating a flow to process an image
imaged by an imaging element.
[0041] FIG. 23 is a view illustrating a flow to process an image
imaged by an imaging element.
[0042] FIG. 24 is a view illustrating a flow to process an image
imaged by an imaging element.
[0043] FIG. 25 is a view illustrating a flow to process an image
imaged by an imaging element.
[0044] FIG. 26A is a view illustrating an example of an image
imaged by a vehicle camera.
[0045] FIG. 26B is an explanatory view explaining a method for
processing an imaged result.
MODE FOR CARRYING OUT THE INVENTION
[0046] Hereinafter, preferred embodiments of this invention will be
described in detail based on the drawings.
[0047] An imaging element according to an embodiment of the present
invention includes, as illustrated in FIG. 1, a light receiving
surface 15b having pixels, a low-pass filter device 14 such as a
low-pass filter, a filter array having a low-pass filter (LPF)
function or the like configured to focus predetermined light on a
predetermined pixel or predetermined pixels of the pixels of the
light-receiving surface 15b. The imaging element according to an
embodiment of the present invention may be used in an imaging
apparatus. The imaging apparatus may include a lens system 13 (11),
the imaging element configured to image a subject to form a subject
image via the lens system, and a control device (not shown)
configured to process the subject image as image data.
First Embodiment
[0048] FIG. 1 is a configuration diagram illustrating an imaging
optical system including an imaging element according to an
embodiment of the present invention. A left side of FIG. 1
indicates a subject side and a right side of FIG. 1 indicates an
imaging plane side. Reference number 11 indicates a lens system 11
formed by one or more lenses, reference number 12 indicates an
aperture stop to set an F number within about 1 to 3, reference
number 13 indicates a lens system formed by one or more lenses, and
reference number 15 indicates an imaging element body. The lens
system 11 is disposed at the subject side from the aperture stop 12
and the lens system 13 is disposed at the imaging plane side from
the aperture stop 12. The lens system 11, the aperture stop 12 and
the lens system 13 are disposed on an optical axis L.
[0049] On the optical axis L, the low-pass filter 14 and the
imaging element body 15 are disposed in order from a side close to
the lens system 13. In this embodiment, the imaging element body 15
may be separately provided or integrally provided with the low-pass
filter 14
[0050] Next, structures of the imaging element body 15 and the
low-pass filter 14 will be explained in detail.
[Imaging Element Body 15]
[0051] As the imaging element body 15, a known monochrome sensor
such as a CCD, a CMOS, or the like may be used. The imaging element
body 15 is protected by a package 15c depending on an intended use
and a lens-side surface of the package 15c is sealed by a cover
glass 15a. A light-receiving part 15b as the light-receiving
surface is provided at a center portion of the package 15c sealed
by the cover glass 15a. The light-receiving part 15b may have
pixels each having a size of predetermined micrometers, for
example, about 1 to 9 micrometers, and the light-receiving part may
have hundreds of thousands pixels or about 10 million, as recently
used. As the package 15c, a high thermally resistant package may be
selected for using as a vehicle camera or an outdoor monitoring
camera, and a small size package may be selected for using as a
portable devices.
[Low-Pass Filter 14]
[0052] The low-pass filter 14 may be configured to extract a
wavelength component of the predetermined light when focusing the
predetermined light on the predetermined pixel or predetermined
pixels of the light-receiving surface 15b.
[0053] The low-pass filter 14 is formed by a flat glass plate or a
resin substrate having surfaces opposite each other, each surface
being provided with diffracting structures.
[0054] FIG. 2A is a perspective view illustrating an end portion of
the low-pass filter, viewed from a side of the lens systems. One
end surface of the low-pass filter 14, which is disposed at the
side close to the lens system 13, is divided into a plurality of
areas 21a, 21b, . Each area 21a, 21b, . . . is configured to focus
light transmitting the low-pass filter 14 on a plurality of pixels,
for example, 4 pixels.times.4 pixels=16 pixels, of the
light-receiving part 15b of the imaging element body 15.
[0055] In each area 21a, 21b, , a concentric circular diffracting
area 22a, 22b, . . . is formed. The diffracting area 22a is formed
by a plurality of concentric circular bands about an optical axis
23a as a center, and the diffracting area 22b is formed by a
plurality of concentric circular bands about an optical axis 23b as
a center. A pitch (an interval) between the circular bands of a
center part differs from that of a peripheral part to modulate the
pitches between the circular bands. According to such a modulation,
the diffracting areas 22a, 22b can have a lens function.
Light-focusing capability becomes higher with decreasing the pitch
or the interval between the circular bands.
[0056] FIG. 2B is a perspective view illustrating an end portion of
the low-pass filter 14, viewed from a side of the imaging element
body 15. The other end surface of the low-pass filter 14, which is
disposed at a side close to the imaging element body 15, is divided
into a plurality of areas 24a, 24b, . . . Each area 24a, 24b, . . .
has a same area and each area 24a, 24b, . . . is configured to
focus light transmitting the low-pass filter 14 on a plurality of
pixels, for example, 4 pixels.times.4 pixels=16 pixels of the
light-receiving part 15b of the imaging element body. The areas
24a, 24b, . . . are disposed substantially at opposite positions of
the areas 21a, 21b, . . . , respectively.
[0057] In each area 24a, 24b, . . . , a concentric circular
diffracting area 25a, 25b, . . . is formed. The diffracting area
25a is provided with a plurality of concentric circular bands about
an optical axis 26a as a center and the diffracting area 26a is
provided with a plurality of concentric circular bands about an
optical axis 26b as a center.
[0058] FIG. 2C is a sectional view illustrating a section of the
low-pass filter 14, viewed in a direction shown by arrow A of FIG.
2A. Sectional shapes of the diffracting structures are rectangular
and the optical axes 23a, 26a of the diffracting areas are disposed
so as to slightly deviate upwardly or downwardly from each other.
Effective diameters of the diffracting areas 22a and 25a differ
from each other and modulated degrees of the pitches and groove
depths of the diffracting areas 22a and 25a are also different from
each other. By use of the shapes of the one end surface and the
other end surface of the low-pass filter 14 differing from each
other, light beams transmitting the areas 21a, 21b, . . . and the
areas 24a, 24b, . . . are focused on different two point on the
light-receiving surface 15b of the imaging element body 15,
depending on the wavelengths of the light beams.
[0059] As a method for producing the low-pass filter, a method
applying a photolithographic technology or a method using precision
cutting process with, for example, a diamond bite, may be used. The
low-pass filter may be produced by forming a pattern in a die
having a shape and performing an injection moulding or a so-called
2P method with a transparent material to copy a plurality of
diffracting optical elements.
[One End Surface of the Low-Pass Filter, Disposed at the Side Close
to the Lens System]
[0060] The diffracting areas 22a, 22b, . . . of the one end surface
of the opposites surface of the low-pass filter 14, which is
disposed at the side close to the lens system 13 have a function as
a spatial low-pass filter for a light beam having a wavelength of
650 nm. Here, the area 21a will be explained as a representative
example. As shown in FIG. 3A, the diffracting area 22a formed in
the area 21a is configured to emit a 0-order diffraction light when
light having a wavelength of 450 nm or 550 nm enters the
diffraction area 22a of the low-pass filter, that is, the
diffracting area 22a is configured to transmit the light as a dead
zone transmission and focus the transmitting light on a
light-receiving area 31a as a part of the light-receiving part 15b
of the imaging element body 15. The light-receiving area 31a
corresponds to an area having 16 pixels. On the other hand, when
light having a wavelength of 650 nm enter the low-pass filter, as
shown in FIG. 3B, the light is emitted as a first diffraction light
and focused on one pixel 32a on the light-receiving part 15b.
Accordingly, the one end surface of the low-pass filter 14 is
configured to function as a mere transmitting element for the light
having the wavelengths of 450 nm and 550 nm and function as a
diffracting element for the light having the wavelength of 650
nm.
[Groove Depth of the Diffracting Area 22a, or the Like]
[0061] The above-described wavelength selectivity can be achieved
by selecting a groove depth of the diffracting structures. By
setting a periodic phase difference of concave-convex shapes in
section of a diffracting grating to be 2n times (multiples of two)
of a predetermined wavelength (for example, 450 nm, 550 nm) of a
predetermined light which is desired to be selectively transmitted
by the low-pass filter, a high 0-order light transmissivity can be
achieved for the light having the wavelengths of 450 nm and 550 nm.
FIG. 4 is a view illustrating a relationship between the 0-order
light transmissivity or the first order light diffraction
efficiency of the diffracting grating having the sectional
concave-convex shapes and the groove depth of the concave-convex
shapes for the wavelengths of 450 nm, 550 nm, and 650 nm. Material
for the used diffracting grating is quartz having a refractive
index of 1.45.
[0062] As seen in FIG. 4, at the depth of about 5.88 .mu.m, the
0-order light transmissivity for the wavelength of 450 nm and 550
nm is 90% or more and the first order light diffraction efficiency
for the wavelength of 650 nm is about 6%. For example, by setting
the groove depth of the diffracting area 22a to be in the
above-described condition, the light having the average (the light
transmissivity of 6% per pixel for 16 pixels, that is, the light
transmissivity of 96%) of the wavelength of 650 nm, transmitting
the area 21a is focused on the pixel 32a shown in FIG. 3B. On the
other hand, the light of 450 nm, 550 nm, and 650 nm are
substantially uniformly received by the pixels of the
light-receiving part 31a other than the pixel 32a.
[Other End Surface of the Low-Pass Filter, Which is Disposed at a
Side Close to the Imaging Element Body]
[0063] The other end surface of the low-pass filter 14, which is
disposed at a side close to the imaging element body has the
diffracting areas 25a, 25b, Each diffracting area 25a, 25b, . . .
functions as a spatial low-pass filter, mainly for the light having
the wavelength 550 nm. Here the area 24a will be explained as a
representative example. The diffracting area 25a formed in the area
24a is, as shown in FIG. 5A, configured to emit substantially a
0-order diffraction light when the light having the wavelength of
450 nm and 650 nm enter the diffracting area 35a, that is, the
diffracting area 25a transmits the light having the wavelengths of
450 nm and 650 nm as a dead zone transmission and focuses the
transmitting light on the light-receiving area 31a of a part of the
light-receiving part 15b of the imaging element body 15. The
light-receiving area 31a corresponds to an area of 16 pixels. On
the other hand, when the light having the wavelength of 550 nm
enters the low-pass filter 14, as shown in FIG. 5B, the first order
diffraction light is focused on one pixel 32b on the
light-receiving part 15b of the imaging element body. Accordingly,
the other end of the low-pass filter 14 is configured to function
as a mere transmitting element for the light having the wavelengths
of 450 nm and 650 nm and function as a diffracting element for the
light having the wavelength of 550 nm. In this embodiment, the
optical axis 26a of the diffracting area 25a is positioned so as to
obliquely deviate by one pixel in a focused position from the
optical axis 23a of the diffracting area 22a
[Groove Depth of the Diffracting Area 25a, or the Like]
[0064] The above-described wavelength selectivity can be achieved
by selecting a groove depth of the diffracting structures. By
setting a periodic phase difference of concave-convex shapes in
section of a diffracting grating to be 2n times (multiples of two)
of a predetermined wavelength (for example, 450 nm, 650 nm) of a
predetermined light, which is desired to be selectively transmitted
by the low-pass filter, a high 0-order light transmissivity can be
achieved for the light having the wavelengths of 450 nm and 650 nm.
FIG. 6 is a view illustrating a relationship between the 0-order
light transmissivity or the first order light diffraction
efficiency of the diffracting grating having the sectional
concave-convex shapes and the groove depth of the concave-convex
shapes for the wavelengths of 450 nm, 550 nm, and 650 nm. Material
for the used diffracting grating is quartz having a refractive
index of 1.45.
[0065] As seen in FIG. 6, at the depth of about 5.81 .mu.m, the
0-order light transmissivity for the wavelength of 450 nm and 650
nm is 90% or more and the first order light diffraction efficiency
for the wavelength of 550 nm is about 7%. For example, by setting
the groove depth of the diffracting area 25a to be in the
above-described condition, the light having the average (the light
transmissivity of 7% per pixel for 16 pixels, that is, the light
transmissivity of about 100%) of the wavelength of 550 nm,
transmitting the area 25a is focused on the pixel 32b shown in FIG.
5B. On the other hand, the light of 450 nm, 550 nm, and 650 nm are
substantially uniformly received by the pixels of the
light-receiving part 31a other than the pixel 32b.
[0066] By using the above-described low-pass filter 14 having the
wavelength selectivity within the optical system, for example, of
the light transmitting the areas 21a and 24a of the front and rear
surfaces of the low-pass filter, the light having the wavelength of
650 nm is focused on the pixel 32a on the light receiving area 31a
of the imaging element body 15 and the light having the wavelength
of 550 nm is focused on the pixel 32b. The light beams having the
wavelengths 450 nm, 550 nm, and 650 nm uniformly enter the pixels
other than the pixels 32a and 32b. Under such a receiving state, an
color image can be formed from a monochrome image by the
reconstruction processes described below with reference to, for
example, FIGS. 8 to 11.
[0067] In this embodiment, the three wavelengths of 450 nm, 550 nm,
and 650 nm are used but the wavelengths are not limited thereto.
For example, a combination of wavelengths of 470 nm, 520 nm, and
600 nm can be used. Furthermore, a case where each wavelength does
not have one value, that is, may have a bandwidth, for example, of
about 20 nm. The combination of wavelengths can have further a
near-infrared wavelength band, for example, about 850 nm in
addition to the three wavelengths.
[0068] Each area 21a, 21b, 24a, 24b and each diffracting area 22a,
22b, 25a, 25b may have a size variation (corresponding to a number
of pixels) depending on a position thereof. That is, the sizes of
the areas 21a, 21b, 24a, and 24b may be varied depending on the
positions from a center of an optical axis of an imaging lens or
the aperture stop to a peripheral area (an area out of the optical
axis).
[0069] Although, as the sectional shape of the diffracting grating,
the rectangular shape in section is described in this embodiment,
the sectional shape of the diffracting grating may have a stepped
structure. Furthermore, the diffraction order is not limited to the
0-order light and the first diffraction light and a second order
light or a higher order light may be used. Moreover, the optical
axes 23a, 26a, 23b, and 26b of the diffracting areas of the front
and rear side surfaces of the low-pass filter may be coaxial. In
this case, the focusing positions of the diffracting areas 22a, 25a
and the diffracting areas 22b, 25b are set to deviate from each
other in a phase difference function. Furthermore, although the
case where the low-pass filter 14 has two end surfaces each having
the diffracting structure is described in this embodiment, the
diffracting structure may be formed on only one end surface. In
this case, the wavelength selectivity can be achieved by use of a
difference in the diffraction order, that is, it can be achieved,
for example, when the light having the wavelength of 650 nm is
focused on a pixel as a + first order light and the light having
the wavelength of 550 nm is focused as a - first order light on a
pixel different from the pixel where the + first order light is
focused.
[0070] The structure of the diffracting area is not limited to the
concentric circular pattern and a liner pattern may be used. In
this case, the diffraction light is focused on the imaging element
body not as a point but a line and therefore, the image
reconstruction can be achieved according to the liner pattern.
[0071] In addition, although the case where the low-pass filter 14
is disposed separately from the imaging element body and between
the lens system 13 and the imaging element body 15 is described, it
is not limited thereto. For example, as a substitute for the cover
glass 15a of the imaging element body 15, the low-pass filter may
be used. Thereby, a number of parts can be reduced. Alternatively,
the low-pass filter may be formed on a lens surface of the lens
system 13. Moreover, the low-pass filter may be formed integrally
with the light-receiving part 15b. In this case, positional
misalignment of the imaging element body or the like can be reduced
to achieve a stable property.
[0072] Hereinafter, a structure of a filter array of the imaging
element will be explained. As shown in FIG. 7, every array period
of 6.times.6 has a pixel having a function of extracting a
wavelength component of red light and a pixel having a function of
extracting a wavelength component of blue light, which are disposed
at a center of the array period. Here, the pixel having the
function of extracting the wavelength component of red light is
referred to as the red filter, and the pixel having the function of
extracting the wavelength component of blue light is referred to as
the blue filter. However, it is not only limited to the case where
there is an actual filter to transmit only the wavelength
component, but also the case where the above-described diffracting
element is used as a filter. In the filter array of FIG. 7, color
filter arrays are continuously disposed at a 6.times.6 pixel
period.
[0073] The pixels of the imaging element may be divided into a
plurality of periods each having an anomalous pixel. The filter
array may have an LPF characteristic such that a light amount of a
light beam focused on the anomalous pixel configured to extract a
predetermined wavelength component is larger than an average light
amount of light beams of the predetermined wavelength component
focused on pixels adjacent to the anomalous pixel entering within
one period of the pixels of the imaging element.
[0074] The pixels other than the pixels of the red and blue filters
do not have a filter function but are configured to obtain
brightness information and therefore are referred to as Y pixels
hereinafter. The important point is that the R (red) pixel of the
red filter and the B (blue) pixel of the blue filter have a spatial
LPF effect. Therefore, an average value of an intensity of red
light entering the array of the 6.times.6 and an average value of
an average value of an intensity of blue light entering of the
6.times.6 can be obtained by the red pixel and the blue pixel,
respectively. In a case where there is no LPF (low-pass filter)
effect, even when performing the following processes, a remarkably
large aliasing noise occurs in color signals and therefore an image
quality is largely degraded.
[0075] The pixels having filter functions is provided with the
spatial LPF effect and composing process is performed under the
consideration of the spatial LPF effect so that the above-described
problems can be solved. The process in this case is shown in FIG.
8.
[0076] The above-described control device may be configured to
perform a separation process to separate the subject image formed
by the imaging element into a first image formed by the
predetermined pixels and a second image formed by the other pixels.
The first image may be an image regarding color information and the
second image may be an image regarding brightness information.
[0077] The control device may be configured to perform an image
expansion process to generate a fourth image by expanding the first
image and an image composition process to compose the second and
fourth images to form a third image in addition to the separation
process.
[0078] The control device may be configured to perform an image
conversion process to convert color information of the second and
third images into brightness information and to form a fifth image
having brightness values of RGB in addition to the image expansion
process and the image composition process.
[0079] The control device may be configured to perform an image
expansion process to expand the first image to form a fourth image,
an LPF process to apply an LPF processing to the first image to
form a sixth image by removing high frequency component from the
first image, and an image composition process to compose the fourth
and sixth images to form a third image in addition to the
separation process.
[0080] The control device may be configured to perform an image
conversion process to convert color information of the second and
third images into brightness information to form a fifth image
having brightness values of RGB in addition to the image expansion
process, the LPF process and the image composition process. The LPF
process may be a process to average brightness values of pixels
within a small range in relation to a period in which the
predetermined pixels are arranged. The LPF process may include an
image reduction process and an image expansion process. The third
image may be an image relating to color information.
[0081] At first, a separation process is performed. In the
separation process, signals from the imaging element are separated
into a second image formed by Y pixels and a first image formed by
R pixels and B pixels. At this time, failure parts in the second
image formed by the Y pixels are interpolated by peripheral Y
pixels before the following image composition process and the
second image has a same size (a number of pixels) as the imaging
element. Then, an image expansion process is performed to expand
the first image formed by the R pixels and B pixels such that the
first image has a same size as the second image and then the image
composition process is performed to generate Cb, Cr
(color-difference) signals to form a third image.
[0082] Next, an image conversion process is performed to combine
the second and third image and then generate a fifth image. In the
image conversion process, for example, the following conversion
equations are used.
Cb_out=0.564.times.(B_in-Y_in)
Cr_out=0.713.times.(R_in-Y_in)
[0083] where Y_in is input data of the second image, B_in and R_in
are input signals of B pixels and R pixels of the fourth image, and
Cb_out and Cr_out are output brightness signals and color signals
of the third image.
[0084] In the image conversion process, the Y (brightness) signals
of the second image are combined and by use of signals of the
imaging element, which are obtained from the above-described color
filter array, a color image obtained from the YCbCr signals of the
fifth image can be obtained.
[0085] Here, the process shown in FIG.9 may be performed so that
high quality image with reduction of aliasing noise can be
obtained.
[0086] That is, in FIG. 9, an LPF process to apply an LPF
processing to the second image to obtain a sixth image is added.
Since in this embodiment, the filter array of 6.times.6 is used, a
filter smoothing 6.times.6 pixels is preferably used for the LPF
processing.
[0087] As the LPF processing, as shown in FIG. 10, the image
expansion process and the image reduction process are used so that
high quality image can be achieved. Here, it is preferable that an
image size of the reduced image is a same size as the size of the
first image (that is, a pixel number of anomalous pixels of the
imaging element) and an image size of the expanded image is a same
size of the fourth image. FIG. 11 is shown as a specific example of
the processes shown in FIG. 10.
[0088] Next, different points in quality of the imaged images
between a case where a subject image is imaged by use of the
imaging element provided with a color filter having a spatial LPF
function and a case where a subject image is imaged by use of the
imaging element provided with a color filter without a spatial LPF
function are explained.
[0089] Table 1 (referred to as "Photo 1", hereinafter) shows an
imaged image in the case where the color filter has the spatial LPF
function and Table 2 (referred to as "Photo 2", herein after) shows
an imaged image in the case where the color filter does not have
the spatial LPF function.
[0090] In the case of Photo 1, there is only small color bleed,
high sensitivity can be achieved because most pixels have no color
filter, and a high-resolution image can be obtained. On the other
hand, in the case of Photo 2, there is large color bleed and
resolution of an image is low.
[0091] For comparison, an imaged image in a case where an imaging
element having the conventionally used Bayer arrangement color
filter is used is shown in Table 3 (referred to as "Photo 3",
hereinafter). In Photo 3, especially, as can be seen from parts of
characters, the resolution of Photo 3 is less than that of Photo
1.
[0092] As can be seen from comparison with Photos 2 and 3, Photo 1
has a higher sensitivity and better resolution.
[0093] In the above-described examples, the color filters of R and
B are used but other combinations of color filters, for example, of
G and B, of R, G, and B, of IR (infrared) and B, and the like may
be used.
[0094] Here, for reference, a comparison with a case where a
Circular Zone Plate (CZP) is used will be explained by using Table
4 (referred to as "Photo 4", hereinafter), Table 5 (referred to as
"Photo 5", hereinafter), and Table 6 (referred to as "Photo 7",
hereinafter).
[0095] Photo 4 is an input CZP image, Photo 5 is an image imaged by
using the imaging element according to this embodiment, that is,
the imaging element having the color filter with the spatial LPF
function, and Photo 6 is an image imaged by using the imaging
element having the Bayer arrangement color filter. In Photo 5,
generation of fake color is suppressed and high resolution can be
achieved in comparison with Photo 6.
[0096] In this embodiment, although the period of the filter array
of 6.times.6 is used to gather 1/36 of an R component of the pixel
into the R pixel in the optical LPF, simply, white light has the R
component of 1/3 of total light amount. That is, the brightness of
the R pixel is 1/3 of the brightness of the Y pixel for a white
subject. Accordingly, there is a problem in that S/N of the R
pixels are degraded. In order to solve the problem, in the optical
LPF, the filter array is preferably configured such that each R
component is set to have 3/36, that is, 1/12 to be gathered into
the R pixels. The configuration for the B pixels is preferably the
same.
[0097] It is possible to use a period of the filter array of more
than 6.times.6 in a case where more sensitivity is needed. For
example, in a case where the filter array having the period of
16.times.16 is used, since resolution of the color information is
degraded, color bleed is easily generated in an output image.
[0098] In this case, in the LPF processing, it can be preferable to
perform the reduction process of 1/8 and the expansion process of 8
times, which are factors smaller than the period of the filter
array, rather than the reduction process of 1/16 and the expansion
process of 16 times.
[0099] A result of the LPF processing where the reduction process
of 1/16 and the expansion process of 16 times are performed is
shown in Table 7 (referred to as "Photo 7", hereinafter).
[0100] A result of the LPF processing where the reduction process
of 1/8 and the expansion process of 8 times are performed is shown
in Table 8 (referred to as "Photo 8", hereinafter).
[0101] In the case of Photo 8, reduced color bleed is achieved and
high quality image can be obtained in comparison with the case of
Photo 7. That is, by performing the LPF processing using factors
smaller than the filter array, high quality image can be
obtained.
Second Embodiment
[0102] The low-pass filter may have a polarization-dependent
characteristic changing depending on a polarization direction of
the predetermined light.
[0103] The polarization-dependent characteristic of the low-pass
filter may be a characteristic to transmit only a predetermined
polarization light component
[0104] Next, a second embodiment of the present invention will be
explained. Although the wavelength-selective low-pass filter is
used in the first embodiment, a polarization-selective low-pass
filter is used in this embodiment.
[0105] In this embodiment, as the low-pass filter 14, a diffracting
grating having light-polarization selectivity is formed. At first,
with reference to FIG. 13, transmissive characteristics of light
beams polarized in relation to a birefringent medium will be
explained. FIG. 13 is a view illustrating paths of the light beams
in a case where the light beams enter and transmit the general
birefringent medium. When the light beams enter the birefringent
medium, a direction of the light beams is changed depending on
polarizations of the light beams. That is, as shown in FIG. 13, the
light beam polarized in a direction parallel to a plane of FIG. 13
in relation to the birefringent medium passes through the
birefringent medium without change of the direction. The light beam
is referred to as an ordinary light beam or a normal light beam. On
the other hand, the light beam polarized in a direction
perpendicular to the plane of FIG. 13 in relation to the
birefringent medium passes through the birefringent medium with
changing the direction. The light beam is referred to as an
extraordinary light beam or an anomalous light.
[Polarization-Selective Diffracting Grating]
[0106] Such a polarization-selective diffracting grating using the
birefringent medium will be explained. FIG. 14A is a view
illustrating a surface of the diffracting grating, at a side where
the light beam enters and FIG. 14B is a sectional view along B-B
line of FIG. 14A.
[0107] The diffracting grating shown in FIG. 14B includes an
isotropic medium 81, a birefringent medium 82, and glasses 83
disposed so as to sandwich the isotropic medium 81 and the
birefringent medium therebetween. The birefringent medium 82 has a
plurality of concentric circular bands (see FIG. 14A), and each
circular band has a rectangular shape in section. In the sectional
view along B-B line of FIG. 14A, the birefringent medium has
concave-convex shapes. The isotropic medium 81 has complementary
shapes in relation to the shapes of the birefringent medium and is
in a contact state with surfaces of the concave-convex shapes of
the birefringent medium 82.
[0108] With reference to FIGS. 14A and 14B, a light focusing
function by use of the polarization-selective diffracting grating
will be explained. FIGS. 14C and 14D are views each illustrating a
transmitting state of the light beams according to polarization
directions of polarized light beams. As shown in FIG. 14B, the
birefringent medium 82 has refractive indices of "no" and "ne"
depending on the polarization directions of the light beams
entering the birefringent medium. Here, no is a refractive index
(ordinary refractive index) for the ordinary light beam and ne is a
refractive index (extraordinary refractive index) for the
extraordinary light beam.
[0109] A case where the polarization-selective diffracting grating
is produced by selecting the isotropic medium 81 and the
birefringent medium 82 so as to set a refractive index n1 of the
isotropic medium to be equal to ne will be explained. When the
light beam enters the diffracting grating such that the
polarization direction of the light beam is equal to the
polarization direction of the extraordinary light beam, the
refractive index of the isotropic medium 81 is the same as that of
the birefringent medium so that the light beam can transmits
without any influence. On the other hand, when the light beam
enters the diffracting grating such that the polarization direction
of the light beam is perpendicular to the polarization direction of
the extraordinary light beam, that is, the polarization direction
of the light beam is equal to the polarization direction of the
ordinary light beam, the refractive indices of the isotropic medium
81 and the birefringent medium are different from each other.
Accordingly, the diffraction occurs due to the shapes of boundary
surfaces of the isotropic medium and the birefringent medium 82 of
the diffracting grating and the direction of the light beam is
changed. As shown in FIGS. 14C and 14D, the dead zone transmission
or the light focusing is selected depending on the polarization of
the entering light beam.
[Low-Pass Filter 14]
[0110] The low-pass filter 14 according to this embodiment has the
above-described configuration and function of the
polarization-selective diffracting grating. That is, the low-pass
filter 14 has a sectional structure shown in FIG. 15, in which
diffracting structures 92 are formed on a glass plate or a resin
substrate 91 by use of the birefringent medium. An isotropic medium
93 are complementarily added and the diffracting grating is sealed
with a glass plate or a resin substrate 94. The light beam enters
the sealing glass plate 94.
[0111] FIG. 16 is a perspective view illustrating an end portion of
the low-pass filter 14, viewed from a side of the lens systems. In
this drawing, for sake of simplicity, the glass plate 94 and the
isotropic medium 93 are omitted. The low-pass filter 14 is divided
into a plurality of areas 101a, 101b, . . . each having a same
area. Each area 101a, 101b, . . . is configured to focus light
transmitting the low-pass filter 14 on a plurality of pixels, for
example, 4 pixels.times.4 pixels=16 pixels, of the light-receiving
part.
[0112] In each area 101a, 101b, , . . . , a concentric circular
diffracting area 102a, 102b, . . . is formed. The diffracting area
102a is formed by a plurality of concentric circular bands about an
optical axis 103a as a center, and the diffracting area 102b is
formed by a plurality of concentric circular bands about an optical
axis 103b as a center. A pitch (an interval) between the circular
bands varies from a center part to a peripheral part to modulate
the pitches between the circular bands. According to such a
modulation, the diffracting areas can have a lens function.
Light-focusing capability becomes higher with decreasing the pitch
or the interval between the circular bands.
[0113] As a method for producing the low-pass filter 14, a method
applying a photolithographic technology or a method using precision
cutting process with, for example, a diamond bite, may be used. The
low-pass filter may be produced by forming a pattern in a die and
performing an injection moulding or a so-called 2P method with a
transparent material to copy a plurality of diffracting optical
elements.
[Diffracting Area of the Low-Pass Filter]
[0114] The diffracting areas 102a, 102b, . . . of the low-pass
filter 14 have mainly a function as a spatial low-pass filter for a
light beam having a polarization direction of an ordinary light.
Here, the area 101a will be explained as a representative example.
As shown in FIG. 17A, the diffracting area 102a formed in the area
101a is configured to emit substantially a 0-order diffraction
light when light having a polarization direction of the
extraordinary light beam enters the diffraction area 102a of the
low-pass filter, that is, the diffracting area 102a is configured
to transmit the light as a dead zone transmission and focus the
transmitting light on a light-receiving area 111a as a part of the
light-receiving part 15b of the imaging element body 15 (see FIG.
1). The light-receiving area 111a corresponds to an area having 16
pixels. On the other hand, when the ordinary light beam enters the
low-pass filter, as shown in FIG. 17B, the light beam is emitted as
a first diffraction light and focused on one pixel 112a on the
light-receiving part 15b. Accordingly, the low-pass filter 14 is
configured to function as a mere transmitting element for the
extraordinary light beam and function as a diffracting element for
the ordinary light beam.
[Groove Depth of the Diffracting Area 25a]
[0115] The above-described polarization-selectivity can be achieved
by selecting a groove depth of the diffracting structures, the
refractive index no of the ordinary light beam, the refractive
index ne for the ordinary light beam, and the refractive index n1
for the isotropic medium. By selecting the refractive indices ne
and n1 so as to be ne=n1, the dead zone transmission for the
extraordinary light beam can be achieved.
[0116] FIG. 18 is a view illustrating a relationship between the
0-order light transmissivity or the first order light diffraction
efficiency for the ordinary light beam of the diffracting grating
having sectional concave-convex shapes and the groove depth of the
concave-convex shapes. The refractive indices are no=1.75 and
ne=1.45.
[0117] At the depth of about 1.86 .mu.m, the 0-order light
transmissivity is 90% or more and the first order light diffraction
efficiency is about 7%. For example, by setting the groove depth of
the diffracting area to be in the above-described condition, the
ordinary light beam is focused only on the pixel 112a of FIG. 17B
and the light having the average of the ordinary light passing
through the area 111a. On the other hand, the ordinary light beam
and the extraordinary light beam are substantially uniformly
received by the pixels of the light-receiving part 121a other than
the pixel 112a.
[0118] By using the above-described low-pass filter 14 having the
polarization-selectivity, for example, the light passing through
the area 101a of the low-pass filter 14 is focused on the pixel
112a of the light-receiving area 11a of the imaging element body 15
as the ordinary light beam. On the other pixels, the light of the
extraordinary light beam is uniformly focused. By such a light
receiving or focusing state, the polarized image can be formed by
using a monochrome imaging in the above-described reconstruction
process with reference to FIGS. 8 to 11.
[0119] In this embodiment, although the case where the diffraction
structure is formed at one side, the diffraction structure may be
formed at two sides. That is, as shown in FIG. 19, in addition to
the plate 91 where the diffraction structure 92 of the birefringent
medium is formed, the low-pass filter may have a plate 91' where a
diffraction structure 92' is formed at an opposite side of the
plate 91 and an isotropic medium 93 is added therebetween.
Furthermore, as described in the first embodiment, it is possible
to set each diffracting surfaces such that a focusing position of
each diffracting surface deviate from each other and the ordinary
light beam and the extraordinary light beams are separately
focused.
[0120] Each area may have a size variation (corresponding to a
number of pixels) depending on a position thereof. That is, the
sizes of the areas 101a may be varied depending on the positions
from a center of an optical axis of an imaging lens or the aperture
stop to a peripheral area (an area out of the optical axis).
[0121] Although, as the sectional shape of the diffracting grating,
the rectangular shape in section is described in this embodiment,
the sectional shape of the diffracting grating may have a stepped
structure. Furthermore, the diffraction order is not limited to the
0-order light and the first diffraction light and a second order
light or a higher order light may be used.
[0122] The structure of the diffracting area is not limited to the
concentric circular pattern and a liner pattern may be used. In
this case, the diffraction light is focused on the imaging element
body not as a point but a line and therefore, the image
reconstruction can be achieved according to the liner pattern.
[0123] Although the low-pass filter 14 is disposed separately from
the imaging element body 15 between the lens system 13 and the
imaging element body 15 in this embodiment, it is not limited
thereto. For example, as a substitute for the cover glass 15a of
the imaging element body 15, the low-pass filter may be used.
[0124] Furthermore, the polarization-selective diffracting grating
is not limited to the combinations of the above-described isotropic
material and birefringent material, and a diffracting grating using
a sub-wavelength structure may be used. That is, as shown in FIG.
20, the polarization selectivity can be achieved by superimposing
the diffracting structure 92 having a pitch larger than the
wavelength of the structure formed on the plate 91 with a periodic
structure having a period (.lamda.) shorter than the wavelength. By
using such a method, simple structure of the polarization selective
diffracting grating can be achieved so that low cost and thin
low-pass filter can be achieved.
[0125] The first image may be an image regarding polarization
information and the second image is an image regarding brightness
information.
[0126] Hereinafter, a structure of a filter array of the imaging
element will be explained. As shown in FIG. 21, every array period
of 6.times.6 has a pixel having a filter configured to transmit a
P-polarized light and a pixel having a filter configured to
transmit a S-polarized light at a center of the array period. Other
pixels (referred to as Y pixels) have no filter function. It is
important that the S-polarized filter and the P-polarized filter
have also a spatial LPF effect and therefore, an average value of
an intensity of the S-polarized light entering the array of the
6.times.6 and an average value of an intensity of the P-polarized
light entering of the 6.times.6 pixels can be obtained. In a case
where there is no LPF effect, even when performing the following
processes, a remarkably large aliasing noise occurs in polarization
information and therefore an information amount is largely
decreased. It is not limited to a case where there is an actual
filter configured to transmit a polarized light, and the
above-described diffracting element, an SWS or the like may have a
filter function.
[0127] As the processes in this embodiment, as shown in FIG. 22, a
separation process of anomalous pixels is performed. In the
separation process, signals from the imaging element are separated
into a second image formed by Y pixels and a first image formed by
S-polarized pixels and P-polarized pixels. At this time, failure
parts in the second image formed by the Y pixels are interpolated
by peripheral Y pixels before the following image composition
process and the second image has a same size (a number of pixels)
as that of the imaging element (for example, 640.times.480, as
shown in the above example).
[0128] Then, an image expansion process is performed to expand the
first image formed by the S-polarized pixels and P-polarized pixels
such that the first image has a same size as the second image and
then the image composition process is performed to form a third
image and therefore brightness information and corresponding
polarization information constituting the third image can be
obtained.
[0129] In general, in a case where the polarization information is
used for detecting a wet road surface to prevent a vehicle to be
skidded, the polarization information is not required to have same
resolution as the brightness information, but the brightness
information is required to have high resolution because the
brightness information is used for displaying an image or
performing a road surface detection processing. In this case, the
method in this embodiment is preferable because the high resolution
brightness information and the polarization information having low
resolution but no occurrence of aliasing noise can be obtained by
one imaging apparatus.
[0130] The image composition process may include simply packing the
brightness information and the polarization information having a
same number of pixels each other and then passing the information
to the following devices. The image composition process also may
include assigning or providing the polarization information to the
color difference information to display the color polarization
information.
[0131] FIG. 23 shows an example where the first to third images are
assigned or provided to the actual data. The case where the
above-described filter array is used is more particularly shown in
a process flow of FIG. 24.
[0132] The control device may be configured to perform an image
reduction process to reduce the second image to form a fourth image
and an image composition process to compose the first and fourth
images to form a third image in addition to the separation
process.
[0133] In a case where the brightness information is not required
to have high resolution, a method shown in FIG. 25 is also
preferable. That is, at first, a separation process of anomalous
pixels is performed. In the separation process, signals from the
imaging element are separated into a second image formed by
S-polarized pixels and a first image formed by P-pixels. At this
time, failure parts in the second image formed by the Y pixels are
interpolated by peripheral Y pixels before the following image
composition process and the second image has a same size (a number
of pixels) as the imaging element, for example, 640.times.480
pixels. Then, an image reduction process is performed to reduce the
second image of the brightness information such that the second
image has a same size as the first image formed by the S-pixels and
the P-pixels to form the fourth image. Then the image composition
process is performed to generate a third image constituted by the
brightness information and the corresponding polarization
information from the fourth image and the first image.
[0134] Next, for example, for a vehicle camera or the like, as
shown in FIG. 26A, a color detection function to detect a color of
a traffic light is necessary at an upper side of a screen and a
function of detecting a wet road surface by using the polarization
information is necessary at a lower side of the screen.
[0135] In this case, as shown in FIG. 26B, it may be preferable
that, for example, an upper side of an imaging element is provided
with the filter array of the first embodiment to obtain a color
image and a lower side of the imaging element is formed by the
configuration where the low-pass filter is configured to extract a
wavelength component of the predetermined light when focusing the
predetermined light, or other combinations of the different filter
arrays to be used in each area.
[0136] According to an embodiment of the present invention, since a
low-pass filter configured to focus a predetermined light on a
predetermined pixel on a light-receiving part of an imaging element
is provided, high resolution and sensitivity of the imaging element
can be achieved. Moreover, ratio of pixels without filter can be
increased as well as the imaging element capable of achieving a
normal color reproduction can be provided.
* * * * *